<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<style>
.box{
  width: 300px;
  height: 300px;
  background-color: aqua;

}
img{
  /* position: absolute; */
  position: fixed;
  top:0;
  left:0;

}
</style>
<body>
  <div class="box"></div>
  <img src="./images/tianshi.gif" id="img" alt="">
</body>
<script>
var img=document.getElementById('img');
// var box=document.
document.onmousemove=function(e){
   var x=e.pageX;
   var y=e.pageY;
   img.style.top=y+'px';
   img.style.left=x+'px';
}

</script>
</html>